Lens system for LED lights

ABSTRACT

An optical device for distributing light produced by a white LED or other light-producing device includes a lens portion that refracts the light to provide a desired light intensity distribution, and a collimating portion that internally reflects light from the white LED. The optical device may be molded from an acrylic polymer material or the like. The reduced thickness of the device facilitates low cycle times and reduces warpage or other distortion that would otherwise be generated during the molding process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/910,691, filed on Apr. 9, 2007, entitled LENS SYSTEM FOR LED LIGHTS,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

“White” LEDs have been used in numerous devices/applications such asflashlights, task lights for motor vehicles and the like. White LEDsgenerally include a blue LED with a phosphor coating that emits yellowlight which mixes with the blue light to provide light that is perceivedto be primarily white, with a slight bluish tint. Another type of whiteLED utilizes a combination of blue, red, and green LEDs to produce whitelight. Due to the efficiency of white LEDs, the use of white LEDs inapplications such as vehicles and the like having a limited supply ofelectrical power has been increasing.

Although the light produced by a white LED has a color that isacceptable for task lights and the like, the light is typically notfocused enough to provide efficient lighting for such applications.Various lenses, reflectors, collimators and the like have been developedto focus or direct the light from LEDs. Referring to FIG. 1, a prior artcollimator 10 includes a body 11 made of a polymer material. The bodyincludes a flat end surface 12 and tapered side surfaces 13 that givesthe collimator 10 a generally conical shape. A cavity 14 has a generallycylindrical side surface 15, and an open end 16 that receives white LED17. A convex surface 18 faces the white LED 17. The light from white LED17 incident upon cylindrical sidewall 15 refracts from the tapered sidesurfaces 13, and exits the collimator 10 through flat end surface 12.The convex surface 18 reflects light internally from white LED 17 anddirects the light through flat end surface 12.

The collimator 10 of FIG. 1 produces a light intensity distributioncurve 19 illustrated in FIG. 2. Thus, although collimator 10 does directthe light in a beam, the light intensity distribution is quite uneven.Also, although white LEDs generally produce a light having a colorsuitable for use as a task light and the like, white LEDs tend toproduce light having a yellowish tint at the peripheral edges of thelight pattern.

Accordingly, a way to direct and focus light from a white LED in anefficient manner would be advantageous.

SUMMARY OF THE INVENTION

The present invention relates to an optical device that utilizes bothinternal reflection and refraction to distribute light from a white LEDor the like. The optical device includes a body made of alight-transmitting material. The body includes a cavity that receiveslight from a light source such as a white LED. The cavity includessidewall surfaces that are cylindrical or conical, and a base surfacethat is preferably flat. The device further includes a tapered rearsurface extending outwardly away from the cavity. The tapered surface isconfigured such that light incident upon the tapered surface from thecylindrical sidewall of the cavity is reflected internally. The devicefurther includes an outer end surface opposite the cavity and taperedsurfaces. The end surface includes a center portion forming a lens, andouter portions that are generally flat. Light reflected internally bythe tapered rear surface is directed through the outer flat surfaceportions. The flat surface portions are configured to transmit lightwithout significant refraction. The lens surface portion preferablyincludes a convex center portion, and a plurality of concentric ridgesforming a Fresnel lens portion.

The intersection between the cylindrical sidewalls of the cavity and thebase surface of the cavity forms a transition point. Light emitted intothe cavity by a white LED that is incident upon the base surface of thecavity is refracted such that the light exits the lens portion of theopposite surface. Light that is incident upon the cylindrical sidewallsof the cavity is reflected off the tapered surfaces and through the flatouter concentric surface portions.

The lens portion of the opposite surface and of the concentric flatportion, along with the tapered surface, are configured such that thelight reflected internally is reflected back towards the center of thelens, thereby directing the yellow light from the edges of the LED backinto the main portion of the light pattern. In this way, the device notonly produces a light pattern having a relatively uniform lightintensity, but also directs the yellow light back towards the center ofthe light pattern, thereby eliminating the uneven color distributionfound with other collimator systems. The optical device may be moldedfrom a suitable polymer such as an acrylic material. The unique shape ofthe optical device provides a thin cross section, having the overallshape of a flat dish. Because the device is quite thin, mold cycle timesfor fabricating the part can be substantially reduced, thereby reducingthe cost of the optical device. Also, the relatively thin cross sectionof the device substantially reduces the imperfections such as “sinks” orthe like that could otherwise be caused by shrinking, warping, and thelike during the molding process.

The device of the present invention includes a reflective, collimatingportion that directs light emitted transversely from the LED, and a lensportion that distributes and focuses the light projected forwardly fromthe LED. The device provides a light pattern having a uniform intensitydistribution. Still further, the device blends the yellowish portion ofthe light pattern produced by the LED back into the center portion ofthe light pattern, thereby providing a substantially uniform coloracross the light pattern.

These and other features, advantages, and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification and appendeddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 is a partially schematic cross-sectional view of a prior artcollimator and white LED;

FIG. 2 is a graph showing a light intensity distribution of thecollimator of FIG. 1;

FIG. 3 is a cross-sectional view of an optical device according to oneaspect of the present invention;

FIG. 4 is a cross-sectional view of an optical device according toanother aspect of the present invention;

FIG. 5 is a view of the device of FIG. 4, showing the light distributionpattern;

FIG. 6 is a side view of the device of FIGS. 4 and 5 showing ray tracesfor light produced by a light source adjacent the optical device;

FIG. 7 is a color graph showing the light intensity distribution of anoptical device according to one aspect of the present invention;

FIG. 8 is a three-dimensional color graph of the light intensitydistribution of an optical device according to one aspect of the presentinvention;

FIG. 9 is a color graph showing the light intensity distribution for anoptical device according to the present invention; and

FIG. 10 is a three-dimensional color chart of the light intensitydistribution of an optical device according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

For purposes of description herein, the terms “upper,” “lower,” “right,”“left,” “rear,” “front,” “vertical,” “horizontal,” and derivativesthereof shall relate to the invention as oriented in FIGS. 3 and 4.However, it is to be understood that the invention may assume variousalternative orientations and step sequences, except where expresslyspecified to the contrary. It is also to be understood that the specificdevices and processes illustrated in the attached drawings and describedin the following specification are simply exemplary embodiments of theinventive concepts. Hence, specific dimensions and other physicalcharacteristics relating to the embodiments disclosed herein are not tobe considered as limiting.

With reference to FIG. 3, an optical device 1 according to one aspect ofthe present invention includes a body 2 made of a transparent acrylicmaterial, or other suitable light-transmitting material. The body 2includes a tapered outer surface 3 extending from an edge 5 toconcentric end surface 4. Edge 5 is formed by the intersection betweentapered outer surface 3 and a cylindrical sidewall surface 6 of a cavity7 at a base end 8 of body 2. The body 2 is symmetrical about acenterline “A,” such that surface 4 has a ring-like shape. Cavity 7includes a base surface 25 that intersects the cylindrical sidewalls 6at a circular corner or edge 26. A white LED 27 is positioned in, orimmediately adjacent to, cavity 7, and provides a light source or point28. Although LED 27 does not actually produce light from a single point,the white LED 27 will be treated as if it produces light from a singlepoint 28 in order to facilitate discussion of device 1. In theillustrated example, surface 25 is planar. However, surface 25 may benon planar (e.g. convex) also.

The light incident upon sidewall surface 6 of cavity 7 and reflectedinternally by tapered surface 3 is collimated, defining a ring-likecollimating portion designated “C.” Light from LED source 28 that isincident upon surface 25 of cavity 7 is refracted through a lens surface34 forming a lens portion “L” at the center of device 1. Light rays 29,30 and 31 produced by white LED 27 are incident upon the cylindricalsidewall surface 6 of cavity 7. The light rays 29, 30 and 31 travelthrough the body 2 and reflected internally by the tapered outer surface3. In addition to the surface 4, body 2 includes ring-like surfaces 32and 33. The ray of light 29 is reflected off tapered surface 3, suchthat it travels through body 2 and exits at surface 33. Light ray 30 isreflected internally by tapered surface 3, and exits through surface 32.Light ray 31 is reflected internally from tapered surface 3, and exitsthrough flat surface 4. Sidewall surface 6 of cavity 7 may becylindrical, or curved or tapered somewhat, and may form a frustum suchas a shallow truncated cone. Although cavity 7 preferably has acylindrical or truncated cone shape, it will be understood that othershapes may also be utilized to provide the required light intensitydistribution. Surfaces 6 and 3 are configured such that light incidentupon surface 6 from white LED 27 reflects internally from taperedsurface 3, and exits through one of the concentric surfaces 4, 32 or 33.Surfaces 4, 32 and 33 are perpendicular to the axis A, or at a slightangle thereto. Surfaces 4, 32 and 33 may be flat, or they may be curvedor shaped slightly if desired to provide a particular light intensitydistribution. In a preferred arrangement, surfaces 4, 32 and 33 are flatto minimize the refraction of light.

Light from LED 27 that is incident upon base surface 25 of cavity 7 isrefracted and travels through body 2, and exits at convex lens surface34. The base surface 25 of cavity 7 and the convex lens surface 34together define lens portion L of the device 1. The corner or edge 26formed by the intersection of the base surface 25 of cavity 7 and thesidewall surface 6 of cavity 7 defines a transition point between thelens portion L and the collimating portion “C” of the device 1. It willbe apparent that the shape of the concentric lens 34 can be selected toprovide a desired distribution of light. Similarly, the tapered outersurface 3 and the sidewall surface 6 can also be selected to collimateand distribute light from LED 28 in a desired manner.

The ring-like surfaces 32 and 33 are preferably spaced inwardly fromsurface 4, with cylindrical sidewall portions 36, 37 and 38 extendingbetween the surfaces 4, 32, 33 and the lens surface 34. Thisconfiguration reduces the overall thickness of the body 2, therebyreducing the cycle time required to mold the device 1. Furthermore, thereduced thickness reduces or eliminates distortions, warping, and thelike that would otherwise result during the molding process.

With further reference to FIG. 4, an optical device 50 according toanother aspect of the present invention has a generally flat dish-likeshape that is symmetrical about a centerline A. Optical device 50 has abase end 51 with a cavity 52 having a sidewall 53 and a base wall 54.Sidewall 53 is preferably a frustum such as a truncated cone forming anangle of about three degrees relative to axis A. Sidewall 53 may alsohave curved shape, and need not form a frustum. In the illustratedexample, base surface 54 is flat, and has the shape of a circle.However, surface 54 may also be non-planar (e.g. convex). A white LED 55provides a source of light that is positioned at point 56. White LED 55is treated as if it were a point source of light 56 for purposes of thepresent description, but it will be readily understood that the whiteLED 55 is not a single point of light.

A tapered outer surface 57 internally reflects light from the LED thatis incident upon cavity sidewall surface 53. For example, light rays 58and 59 are incident upon the sidewall surface 53 of cavity 52, andreflected internally from tapered surface 57 and exit at surfaces 61 and62 by the collimating portion “C” of device 50. Surfaces 61 and 62 maybe flat such that they do not substantially affect the distribution oflight reflected from tapered surface 57. In the illustrated example,surface 62 is positioned closer to end 51 of device 50 to thereby reducethe amount of material required to mold the optical device 50.

Light from point 56 that is incident upon surface 54 of cavity 52 isrefracted to a lens surface portion 63 of device 50 formed in the lensportion “L” of device 50. Lens surface portion 63 includes a convex lenssurface portion 64 at the center thereof, and a plurality of concentricridges 65-68 that form a Fresnel lens portion. Light exiting the lenssurface portion 63 is refracted to provide the desired lightdistribution by the convex lens surface 64 and the Fresnel lens formedby concentric ridges 65-68. A circular corner or edge transition 69 isformed at the corner between sidewall surface 53 and base wall surface54. Light incident upon the sidewall surface 53 is reflected internallyby tapered outer surface 57, and exits through a flat surface 61 or 62.However, light incident on surface 54 on the other side of thetransition 69 is refracted internally, and distributed by the lenssurface 63. The shape of lens surface portion 63 may be selected toprovide a desired light distribution (intensity).

The design of the device 50 will vary depending upon the particularapplication and light intensity distribution desired. Nevertheless, theangle θ₁ between the axis A and the transition point 69 will be aboutsixty degrees. Although the angle θ₁ may be somewhat larger or smallerthan sixty degrees, it will be apparent to those skilled in the art thatlight incident upon surface 54 may not refract completely at greaterangles (depending, of course, upon the refractive index of the materialused to form device 50), such that angle θ₁ is preferably notsubstantially greater than sixty degrees. Conversely, if the angle θ₁ issubstantially smaller than sixty degrees, the amount of light from whiteLED 55 that is directed through the lens portion L is relatively small.Because the lens portion L provides control over the light intensitydistribution, control of the total light intensity distribution isfacilitated by having a relatively large percentage of the lightproduced by the LED refracted through lens portion L.

With further reference to FIG. 5, light that is incident upon sidewall53 and reflected internally through tapered outer surface 57 is directedby collimating portion C of device 50 in a pattern bounded by lines 70and 71. Light that is incident upon base surface 54 of cavity 52 isdirected from the lens surface portion 63 in a pattern bounded by theline 72. At an optimal distance from a surface 75, the lines 71 and 72intersect at a point 76, and the line 70 intersects the axis A at apoint 77. In general, the light emitted from the collimating portion “C”(FIG. 4) of device 50 will tend to have yellowish tint due to the yellowtint of the light produced by the white LED that is directed outwardlyonto surface 53 of the collimating portion C of the device 50. Asillustrated in FIG. 5, this light is distributed back towards the centerpoint 77 of the light distribution pattern, thereby alleviating oreliminating the yellow tint that would otherwise occur around theperipheral edges of the light pattern. Also, the shape of the lenssurface portion 63 and the tapered surface 57, as well as the cavitysurface 53 and 54, are selected to distribute the light in a patternthat has a substantially uniform intensity distribution. It will beunderstood that commercially available lens design/ray tracing softwaremay be utilized to design the exact shape of the device 50 as requiredfor a particular application.

Examples of the distribution of light from lens portion 63 is shown bylines 78-80. Ray of light 78 from LED contacts surface 54 at a point 82,ray of light 79 contacts surface 54 at a point 83, and ray 80 contactssurface 54 at a point 84. The rays 78-80 form angles θ₂, θ₃, and θ₄respectively, relative to the centerline A. Thus, light incident onsurface 54 further from center point 81 is distributed outwardly by lensportion 63 at increasingly larger angles relative to the centerline A tothereby distribute light outwardly towards the outer portion of thelight distribution pattern. In contrast, the collimating portion C ofdevice 50 functions such that light from LED 55 that is incident onsurface 53 is refracted from surface 57, and a ray 85 is distributedback towards the center point 77, whereas a ray 86 is distributedtowards the outer portion of light distribution pattern shown at thepoint 76. Thus, light from LED 55 distributed by the collimating portionC of device 50 is directed closer to the center of the target if therays of light are at a greater angle relative to centerline A to therebydistribute light having a yellow tint towards the center of the lightdistribution pattern. Thus, the collimating portion of device 50distributes light back towards the center of the light distributionpattern, rather than distributing light further towards the outerportion of the pattern.

FIG. 6 shows a ray tracing simulation of a device according to FIG. 4.FIGS. 7-10 show simulated light intensity distributions of devicesaccording to the present invention. One example of such commerciallyavailable software is Trace Pro® software, available from LambdaResearch Corporation of Littleton, Mass. The light intensity patternsshown in FIGS. 7-10 are the result of a commercially available raytracing program utilized to design and model the lens 50. As shown inFIGS. 7-10, the device of the present invention provides a lightintensity distribution that is substantially more uniform than thepattern produced by known collimators and the like. FIGS. 7 and 8 showthe entire illuminance map for a lens according to the presentinvention, and FIGS. 9 and 10 show a close-up of a center portion of theilluminance map of a lens device according to the present invention.Testing has shown that actual devices constructed according to thearrangement shown in FIGS. 4 and 5 provide a very uniform lightintensity distribution. The actual devices may have a slightly differentlight distribution than the simulated light distributions shown in FIGS.7-10 due to imperfections in the material of device 1, and/or thesurface shapes of device 1 and the like. Nevertheless, the lightintensity distribution of the actual devices closely corresponds to thesimulated results. The light intensity distribution of the actualdevices may be more uniform than the simulated results due to suchimperfections. Significantly, the device of the present invention iscapable of providing a light intensity distribution that is perceived tobe substantially uniform to a viewer.

FIGS. 7 and 8 are the light intensity of the device/lens of FIG. 6 on atarget surface having a 600 mm diameter, and FIGS. 9 and 10 are thelight intensity of the device/lens of FIG. 6 on a 300 mm diameter targetsurface. The device of FIG. 6 is substantially the same as the opticaldevice 50 of FIGS. 4 and 5. In the illustrated example, device 50 isdesigned to illuminate a target area having a diameter of 300 mm at apredetermined distance from the target surface. The target area could,of course, be larger or smaller depending upon the requirements of aparticular situation. As shown in FIGS. 9 and 10, the device 50 providesa relatively uniform light intensity across the 300 mm diameter targetsurface. With reference to FIG. 9, other than a small band or ringdirectly adjacent the outer edge of the light distribution pattern, thelight intensity varies from about 60 lux to about 135 lux. Furthermore,a substantial majority of the area of the light intensity pattern ofFIG. 9 is about 80 lux to about 100 lux.

As shown in FIGS. 7 and 8, device 50 also provides a substantiallyuniform light intensity distribution over a 600 mm diameter targetsurface. Although the light intensity is reduced somewhat around theouter edge of the 600 mm target, even at the edge portions the lightintensity is relatively uniform, without the fall off found, forexample, in the prior art device 10 as shown in FIG. 2. With referenceto FIG. 7, the substantial majority of the light intensity pattern isabout 50 lux to about 100 lux. Thus, the lens device of the presentinvention provides a light intensity distribution that varies by no morethan about a factor of two across the majority of the area of the lightintensity distribution.

It will be understood that the exact shape, size, and other features ofa device according to the present invention will depend upon the sizeand shape of the area that is to be illuminated, as well as the distancefrom the light source to the work surface or other surface beingilluminated. Furthermore, it will be apparent to those skilled in theart that the exact shape of the device may vary somewhat, yet stillutilize the essential features of the invention, and providesubstantially similar benefits to those described in connection with thedevices of FIGS. 3 and 4. For example, the number of concentric ridgesused to form the Fresnel portion of the lens of the device of FIG. 4 mayvary, yet still provide the desired light intensity distribution, andalso provide a device which can be rapidly molded.

Also, different combinations of surface shapes may be utilized toprovide the required light intensity distribution. For example, if thesidewall 53 of cavity 52 (FIG. 4) is not conical or cylindrical, butrather has a curved shape, the outer surface 57 may have a differentcontour to “compensate” for the shape of sidewall 53 to provide therequired light intensity distribution. Also, although surface 54 ofcavity 52 is preferably planar, surface 54 could have a non-planarshape, and the lens surface portion 63 could have a shape that, togetherwith a non-planar surface 54, provides a generally uniform lightintensity.

The optical device of the present invention provides a cost effectiveway to distribute light from a white LED or other light-producingdevice. The device utilizes a lens portion which focuses and distributeslight from the LED, and also includes a portion that reflects lightinternally and thereby collimates the light. An optical device accordingto the present invention provides a way to reduce or eliminate theyellow tint produced by white LEDs at the edges of the light pattern.

In the foregoing description, it will be readily appreciated by thoseskilled in the art that modifications may be made to the inventionwithout departing from the concepts disclosed herein.

1. A light assembly, comprising: a LED light source; a lens including a body defining a front side and a rear side and formed of a light-transmitting material, the rear side of the body having a generally frustum-shaped cavity defining a first inner surface portion facing the LED, wherein the first inner surface portion is generally conical, and a base inner surface portion defining a rear lens surface facing the LED, the body further defining a tapered outer surface on the rear side of the body, the body further defining a front surface on the front side of the body, the front surface including a front lens surface portion having a convex surface and a collimating front surface portion extending around the front lens surface portion, wherein the collimating front surface portion includes a ring-shaped planar portion, first and second ring-shaped planar portions, and an inwardly-facing transverse surface extending between the first and second ring-shaped planar portions; and wherein: a first portion of the light from the LED light source travels into the body through the rear lens surface, and escapes from the front lens surface portion, a second portion of the light from the LED light source travels into the body through the first inner surface portion, is internally reflected within the body at the tapered outer surface, and escapes from the body through the collimating front surface portion, and the first and second portions of the light at least partially combine after escaping from the body and define a target area that is spaced-apart from the body, and wherein the first and second portions of the light together provide a generally uniform light intensity distribution over a substantial majority of the target area.
 2. The light assembly of claim 1, wherein: the transverse surface is substantially cylindrical.
 3. A light assembly, comprising: a LED light source; a lens including a body defining a front side and a rear side and formed of a light-transmitting material, the rear side of the body having a generally frustum-shaped cavity defining a first inner surface portion facing the LED, wherein the first inner surface portion is generally conical, and a base inner surface portion defining a rear lens surface facing the LED, the body further defining a tapered outer surface on the rear side of the body, the body further defining a front surface on the front side of the body, the front surface including a front lens surface portion having a convex surface and a collimating front surface portion extending around the front lens surface portion; a first portion of the light from the LED light source travels into the body through the rear lens surface, and escapes from the front lens surface portion; a second portion of the light from the LED light source travels into the body through the first inner surface portion, is internally reflected within the body at the tapered outer surface, and escapes from the body through the collimating front surface portion; the first and second portions of the light at least partially combine after escaping from the body and define a target area that is spaced-apart from the body, and wherein the first and second portions of the light together provide a generally uniform light intensity distribution over a substantial majority of the target area; and wherein: the front lens surface portion includes a plurality of concentric raised ridges extending about the convex surface, and wherein the first portion of the light from the LED escapes from the raised ridges without being internally reflected.
 4. A light distributing device, comprising: a lens including a body defining a front side and a rear side and formed of a light-transmitting material, the rear side of the body having a rearwardly-facing cavity having a first inner surface portion that is generally conical, and a base inner surface portion defining a generally planar rear lens surface, the body further defining a tapered outer surface on the rear side of the body facing outwardly and rearwardly, the body further defining a front surface on the front side of the body, the front surface including a central portion defining a non-planar convex front lens surface portion, wherein the front lens surface portion includes a plurality of concentric raised ridges extending about the convex surface, the front surface further including a collimating front surface portion extending around the front lens surface portion; wherein a first portion of light from a light source positioned proximate the cavity travels into the body through the rear lens surface, and escapes from the front lens surface portion, and a second portion of light from a light source positioned proximate the cavity travels into the body through the first inner surface portion, is internally reflected within the body at the tapered outer surface, and escapes from the body through the collimating front surface portion; and wherein: the first and second portions of light together form a beam of light defining an area at a predefined distance from the lens, the area including a central portion comprising a substantial majority of the area, and wherein the beam of light has a light intensity distribution that is substantially uniform across the central portion of the area, and drops off sharply in a peripheral edge portion of the area extending around the central portion of the area. 